Soldier and law enforcement personnel use night vision devices, e.g. the AN/PVS-14, that include an image intensifier tube to allow them to see under very low light conditions. Before these devices are sent out on a mission they need to be tested to ensure they work properly. The most widely used image intensifier test set is the TS-4348/UV “Test Set, Electronic Systems” (a.k.a “Assessor”) and has been in production since approximately 1992 (see FIG. 1). The TS-4348/UV is compact and lightweight. The functionality of the TS-4348/UV is controlled by MIL-PRF-49318A which states “The Assessor is a self-contained, battery operated, test device designed to provide a Go/No-Go check of the night vision systems . . . . ” The Go/No-Go check is accomplished by projecting a USAF 1951 bar target (a sample is shown in FIG. 2) into a night vision system, at controlled light levels, in a manner that allows the resolution of the night vision system to be measured near the optical axis. The TS-4348/UV uniformly illuminates the field of view of the night vision system under test and illumination intensity is electronically controlled with precise opto-electronic feedback. The TS-4348/UV does not provide a means to identify defect (black spot and white spots) location or size, or for performing off-axis resolution tests.
The most common current method of identifying and measuring defects is with the use of a paper chart approximately 22.5″×30″ in size (see FIG. 3) mounted on a wall. The test involves holding a night vision device 30″±1″ from the chart, viewing perpendicular to the chart, and centered on the concentric circles in a room whose light level can be adjusted from bright to dark. Black spots are identified with the room lights on, white spots are identified with the room completely dark, and other defects when the light level is low. Once defects are identified, the concentric rings are used to identify the zone in which the defect falls. The device is then repositioned to place the defect next to the black circles on the target which allow for defect size measurement. The number of defects and zones in which they fall are compared to a specification to determine the acceptability of the tube in a Go/No-Go style test. The wall chart does not provide a resolution test and requires a room with controllable lighting.
The Hoffman ANV-126A (see FIG. 4) is a high end night vision tester with significantly more functionality than the TS-4348/UV or a wall chart. The ANV-126A performs resolution testing with a USAF 1951 bar target similar to the TS-4348/UV but with much greater electronic control over illumination levels and can perform defect zone mapping similar to a wall chart. A number of additional tests, such as measuring tube gain and tube current draw can also be performed which the TS-4348/UV, wall chart cannot perform. The drawbacks are in cost, complexity, and portability; an ANV-126A retails for approximately $40,000 while an Assessor is approximately $1000 and a wall chart less than $100. The weight of an ANV-126A exceeds 20 pounds while both the TS-4348/UV and wall charts are less than 1 pound each. The TS-4348/UV requires batteries to operate and the ANV-126A requires access to AC power. The TS-4348/UV and wall charts are commonly used in Army repair enclosures, such as the AN/ASM-146 or AN/ASM-147, while the ANV-126A is considered unsuitable for those environments.
The modern image intensifier tube dates back to the 1970's and was used in military devices such as the AN/PVS-4 night vision weapon sight and AN/PVS-5 night vision goggle. These early devices used what was referred to as 2nd generation image intensification tubes. Current state of the art night vision devices use 3rd generation image intensification tubes which function on the same principles as the 2nd generation tubes with some evolutionary improvements. Test equipment to evaluate and diagnose night vision devices with image intensification tubes has been developed over the years. Testers include the 1990's vintage TS-4348/UV low light resolution tester, wall charts, or the Hoffman Engineering ANV-126-001 night vision goggle tester, noted above.
Field test equipment is desirable to support logistics. Shipping damage, degradation during shipping, or failed vendor quality checks can lead to a new image intensifier tube being unsuitable prior to use. Good image intensification tubes are expensive and have a limited life span over which their performance will slowly degrade, and it is desirable to identify the point at which a tube has degraded to the point where replacement is merited. Finally, night vision systems are typically used in potentially hostile environments such as by the military, search and rescue, and police, which can result in a night vision system being damaged. When damage occurs, convenient methods and tools to diagnose the damage are needed in order to determine if repairs are needed.